The present invention relates to an image scanner and, more particularly, to an image scanner capable of detecting the center of a valid image reading range.
Today, an image scanner is extensively used to read an image and input it to, e.g., a personal computer. The image scanner usually includes a rotatable mirror and a linear CCD (Charge Coupled Device) image sensor. One line of image in the main scanning direction reflected in the mirror is incident to the linear CCD image sensor. A bidimensional image is read by the scanner with the mirror sequentially rotated in the subscanning direction. Assume that when the mirror is held at an angle of 45.degree., a distance at which an image positioned at an angle of 90.degree., as seen from the image sensor, is incident to the image sensor is the center position of the mirror. Then, when the angle of the mirror is changed, the distance of the image incident to the image sensor is farther than when the mirror is held at the 45.degree. position. As a result, the image is sequentially reduced in size in the main scanning direction as the mirror is moved away from the 45.degree. position. This causes the bidimensional image picked up by the image scanner to distort in a barrel configuration. To correct such distortion, it is necessary to detect the center of an image, i.e. a position where the mirror reaches its 45.degree. position, and then enlarge the image reduced in the main scanning direction to its original position in accordance with the distance from the above position. The prerequisite is therefore that the center of an image be detected. It has been customary to detect the center of an image by using a photointerrupter or similar photosensor responsive to the angle of the mirror or by fixing the start position of the mirror.
However, the problem with the above conventional schemes is that the angular error of the mirror is too great to detect the center with accuracy. This prevents the barrel-like distotion particular to the image sensor to be corrected.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 61-9074, 61-229174, 64-48120, 3-150521, 4-167861, 5-7280, 5-40843, and 9-21970.